Planar charging ink jet printheads use a droplet emitter (known as a droplet generator) and a plurality of droplet deflection electrodes (known as a charge plate) in precise alignment, which create the "ink jet" technology area of a printhead. Current technology presets two degrees of freedom and uses a manipulation fixture to align the other four degrees of freedom. Screws are tightened once the desired relationship is achieved between the drop generator and the charge plate, such as is disclosed and claimed in U.S. Pat. No. 5,475,409.
However, alignment technicians experience difficultly maintaining this precision alignment between the droplet generator and charge plate when torque is applied to the screws that secure the assembly into its final position; this movement being known as an alignment shift. Additional difficulty occurs at alignment via "sticktion." Sticktion occurs between two coplanar surfaces, in this case a droplet generator and charge plate, when a force is applied while translating one to the other. Lastly, alignment shift of another nature occurs with this design in shipping. That is, shifts happen when accelerations as low as 15 g's are introduced into the printhead assembly, such as during shipping.
Prior art attempts to address the mentioned problems propose eliminating the screws that caused shifts. Unfortunately, those screws were also used for alignment, which is necessary. A proposed solution to sticktion involves the use of external precision rigid stages that are nested together and held to a small clearance between the former coplanar surfaces. Cyanoacrylate (CA) is then applied to this gap to set the desired relationship between the droplet generator and the charge plate, such as in U.S. Pat. No. 5,812,164. Shipping alignment shifts were improved, now requiring 50 g's before movement occurred.
Still, problems persist with even the improved prior art approaches. For example, caution and skill must be used to lay (or caulk) adhesive into a groove that loads capillary channels between two slightly gapped surfaces to secure alignment, while avoiding exposure of other printhead hardware and components to the adhesive. In addition, adhesive simply does not feed into the desired cure areas very well. Also, adhesive cure times can be greater than forty-eight hours. During this time the structure is susceptible to alignment shifts.
It is seen, therefore, that a need exists for an improved means for achieving and maintaining alignment of ink jet printhead components, particularly between the droplet generator and the charge plate.